Splitting failure of a composite under longitudinal tension

Abstract

Significant variation can be found in measurements for the longitudinal tensile strength of the same unidirectional (UD) composite. A splitting failure is one of the main reasons. It is shown in this paper that the shear stress component resulted from a longitudinal tension and a fiber misalignment can cause the matrix to fail before fiber break. The misalignment angle consists of an initial off-axial angle and a further fiber rotation during the loading. Based on the micromechanics Bridging Model and the matrix true stress theory established by the author, splitting failure has been analyzed and predicted rigorously in this paper, only using the fiber and matrix properties together with the fiber misalignment angle. The fiber initial misalignment angle of a unidirectional plate can be obtained from testing statistics, or deducing from measured longitudinal compression strength. Our research indicates that the longitudinal tensile strength and the relevant failure mode can be significantly affected by the fiber initial misalignment.

True Stress Theory of Matrix in A Composite: A Topical Review

“…A fiber splitting failure can be analyzed similarly [ 13 ]. The only difference is in that the misalignment increment is positive under a longitudinal compression, but negative under a longitudinal tension [ 13 ].…”

“…It is evident that the load share of the fiber attains the highest when a continuous fiber composite is subjected to a longitudinal load, and thus a fiber fracture can occur most possibly. Even in such a case, however, a fiber splitting failure is often seen at a longitudinal tension ( Figure 2 a), and a fiber kinking failure occurs most frequently at a longitudinal compression ( Figure 2 b [ 12 ]), both of which are caused by a matrix shear failure [ 13 , 14 ]. Due to an inevitable fiber misalignment in a composite fabrication, a longitudinal load generates a shear stress component in the misaligned coordinate system ( Figure 2 c).…”

“…Using the true stress concept, a number of long-standing and challenging problems in composite failures are resolved satisfactorily and easily. They include a necessary and sufficient condition for a fiber and matrix interface debonding to occur given a composite subjected to an arbitrary load [ 8 ], a fiber splitting [ 13 ] or kinking [ 14 ] failure versus a fiber fracture, and a large shear deformation of the composite induced from relative slippage displacements between debonded fiber and matrix interfaces [ 15 ]. All of these failures are analyzed with no iteration.…”

Multiscale analysis method and experiments for the transverse mechanical property of unidirectional fiber-reinforced composites

“…The research results show that the matrix true stress theory can accurately predict the failure and strength behaviors of composites under different load conditions. Zhou and colleagues [37][38][39][40] researched the prediction of interfacial debonding in fiber-reinforced composite laminates, and established an analytical method to estimate the load level when interfacial debonding occurs between the fibers and matrix of a composite under an arbitrary load. The research results show that for a unidirectional composite subjected to an arbitrary load, when the principal stress is positive and the von Mises stress of the matrix reaches the critical value, the applied load level when interfacial debonding occurs is determined accordingly.…”